I have a 2002 Blazer with the center console automatic shifter. I have some questions about Overdrive:

Is Overdrive an on/off thing I can control?

If Overdrive is only while in OD (4th gear), is it safe to manually downshift to 3 if I don't want Overdrive?

Is Overdrive really part of 4th gear, or is it an ordinary 4th gear and then an OD gear?

Is it safe to tow in Overdrive?

Should I be concerned about 3000+ RPM in 3rd while at highway speeds?

 

Tow/Haul mode disables it but i believe only column shifted trucks had that, Do not tow in Overdrive, do not downshift to third from drive instead shift from park to 3rd directly, do not use the normal forward gear at all when towing, and if moving in 4th gear downshifting to 3rd without dropping the tach first will do exactly what you think it will - a metric ton of damage. The high RPM sounds like the torque converter on your rig isnt locking, the gear ratio isnt that far apart. if worried about it then drive in the furthest right lane you can and keep the tach down in 3rd only, as again, Do not tow in Overdrive, Says so in the owners manual as well. Its hard on the transmission and clutches, as well as the hard parts (planetary gear sets, 3rd gear Drum and Sun Shell.) and gets the fluid real hot. a trans cooler might help but its still just not a good idea.

 

my 99 Bravada has the floor shifter. we towed a canoe And 4 tires on arefurbished pop-up trailer-turned-stakeside, so literally all the way around Lake Michigan... Lansing to Wisconsin via Chicago through the u p Iron Mountain and back down. no extra trans cooler. 3rd gear the whole way. RPMs ran about 2700 at highway speed (67ish). no issues.

 

Really? 3rd gear on mine runs nearly 3000 RPM at 60 MPH. Though my '02 Blazer is 4x4, so I guess that makes a difference.

 

depends on rear axle gearing, final gear ratio on transmission, and tire size. Taller gears are better for highway, while short gears are good for acceleration off the line. Most trucks have 3:43 or 3:73 Gearing, i really wish it was easier to re-gear 4WD rigs but it requires doing both front and rear differentials.

 

Yeah, I learned that I have the optional Eaton G80. I believe its ring gear is 7.625 in and 3:73 ratio. My Blazer is equipped like a ZR2, but its not a ZR2.

 

As an addition to the question in the OP, you need Solenoid A to have First gear, so unless you really get good with flipping a manual lockout switch, adding tow haul would be a chore without some relay logic to determine what gear the transmission is in, wouldnt be too hard and given a bit i can come up with something.